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Category: Master Plan

Published: 08 March 2020

The Analemma Society proposal to replicate the Ibn al-Shatir sundial is incorporated in the Fairfax County Park Authority's Master Plan to create an Astronomical Garden representing significan historical sundials and astronomical instruments.  The Analemma Society has selected the Ibn al-Shatir sundial to recognize the milestone of the beginning of modern sundial history.

We go back in time to the founding of Great Mosque of Damascus, the first monumental Islamic work of architecture initially built 709 to 715 CE during the Umayyad Caliphate.  Four centuries later in 1371 the mathematician and astronomer Ibn Al-Shatir created a revolutionary new sundial for the mosque. This is one of the most significant sundials in the history of sundial science for two important reasons.

• The sundial represents the culmination of the Islamic science of astronomical timekeeping, as Ibn al-Shatir was the last and probably the greatest of generations of Islamic astronomers and timekeepers from the Damascus School of Astronomy.
• This sundial represents the invention of a new type of dial design, the first to use a polar gnomon parallel to the earth’s axis which in turn shows equal hours throughout all the days of the year as straight lines on the dial face. This sundial design became the dominant type when introduced to Europe about 75 years later.  Before that time (and actually incorporated into Ibn al-Shatir's dial) dials used horizontal or vertical gnomons casting hourly shadows that had different lengths depending upon the time of year.

Thirty years after al-Shatir created the sundial for call to prayer at the Damascus Mosque, the mosque was burned and the astronomy school disbanded when Timur the Lame (Tamerlane) captured and devastated Damascus in 1401. But the original sundial by al-Shatir, a 2 m x 1m marble slab, still exists in the National Museum of Damascus. A replica made in 1880 (the original broke during cleaning...you can still see the fracture) that remains in the minaret of the Great Mosque to this day.

The sundial shows all five of the Moslem prayer times, even those at dawn and dusk when the sun is well below the horizon.  Three sets of hour lines are drawn on the dial face as well: hours after sunrise, hours before sunset, and the one we typically recognize today, equal solar hours from 6am to 6pm.

The following animation shows what the dial might look like in a minerat arch at Observatory Park.  Watch closely and you can see the polar gnomon cast not only the time of day, but because there is a split in the gnomon where two gnomon pieces nearly touch, a spot of light shows the date.  In the animation you can see the shadow differences between the summer and winter solstices and at the equinoxes.